Firmware that meets the UEFI 2.3.1 specifications provides the following benefits:

Faster boot and resume times.

Ability to use security features such as Secure Boot and factory encrypted drives that help prevent untrusted code from running before the operating system is loaded. For more information, see Secure Boot Overview and Factory Encrypted Drives.

Ability to more easily support large hard drives (more than 2 terabytes) and drives with more than four partitions.

Compatibility with legacy BIOS. Some UEFI-based PCs contain a Compatibility Support Module (CSM) that emulates earlier BIOS, providing more flexibility and compatibility for end users. To use the CSM, Secure Boot must be disabled.

Support for multicast deployment, which allows PC manufacturers to broadcast a PC image that can be received by multiple PCs without overwhelming the network or image server.

Windows 8.1 and Windows® 8 support native UEFI 2.0 or later on 32-bit (x86), 64-bit (x64), and ARM-based PCs. They also support BIOS-based PCs, and UEFI-based PCs running in legacy BIOS-compatibility mode.

Some features such as Secure Boot require UEFI 2.3.1 Errata C or higher.

Windows Server 2012 R2 and Windows Server® 2012 support native UEFI 2.0 or later on 64-bit systems. Some features such as Secure Boot require UEFI 2.3.1.

While in UEFI mode, the Windows version must match the PC architecture. A 64-bit UEFI PC can only boot 64-bit versions of Windows. A 32-bit PC can only boot 32-bit versions of Windows. In some cases, while in legacy BIOS mode, you may be able to run 32-bit Windows on a 64-bit PC, assuming the manufacturer supports 32-bit legacy BIOS mode on the PC.

Windows supports a subset of the functionality that is defined in the UEFI specification. Windows implementations do not explicitly check against higher revisions of the firmware

For some platforms or hardware configurations, you may need to perform additional steps to make sure that Windows is installed in UEFI mode or in legacy BIOS-compatibility mode. For more information, see Boot to UEFI Mode or Legacy BIOS mode.

UEFI hard disks require the GUID partition table (GPT) partition structure, instead of the master boot record (MBR) partition structure that is used in BIOS.

When you install Windows by using the Windows product DVD, Windows Setup detects whether the PC was booted in UEFI mode or BIOS-compatibility mode, and it configures Windows based on this selection.

Windows Preinstallation Environment (Windows PE) can be configured to support both UEFI mode and BIOS-compatibility mode.

Note

While the PC is in UEFI mode, the Windows PE version must match the PC architecture. A PC in 64-bit UEFI firmware mode can only boot 64-bit versions of Windows PE. A PC in 32-bit UEFI firmware mode can only boot 32-bit versions of Windows PE. On PCs that support both UEFI mode and legacy BIOS mode, you may be able to run 32-bit Windows PE on a 64-bit PC by changing BIOS menu settings from “UEFI mode” to “BIOS mode”, assuming the manufacturer supports legacy BIOS mode.

Note to firmware manufacturers: Do not use tools or applications to alter Windows-specific boot files, including files in the C:\boot and C:\EFI folders. Altering these files could interfere with the PC’s ability to boot up, to resume from hibernation, or to run system recovery tools. Instead, use tools such as BCDboot to set the boot order. For more info, see BCDboot Command-Line Options.